A mixture of solids at Sua pan contains anhydrous sodium carbonate. To determine its percentage purity, 8 g of the mixture was dissolved in water and the solution was made to 500 cm³. 25 cm³ of this solution is neutralised by 40 cm³ of 0.1 mol/dm³ hydrochloric acid (methyl orange indicator). Na₂CO₃(aq) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)

1. aCalculate the number of moles of the acid in 40 cm³ of 0.1 mol/dm³ hydrochloric acid. [2]
2. bCalculate the number of moles of sodium carbonate in 25.0 cm³ of the solution. [1]
3. cCalculate the number of moles of sodium carbonate in 500 cm³ of solution. [2]
4. dCalculate the mass of sodium carbonate in 8 g of the mixture (Mr Na₂CO₃ = 106). [1]
5. eCalculate the percentage purity of sodium carbonate found in the mixture at Sua pan. [1]

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